1. Field of the Invention
The present invention relates to power driven exercise treadmills and more particularly to such treadmills wherein the moving tread belt is a power driven endless belt having a variable but nominally constant speed and also variable means by which dynamic, incremental changes in belt speed occur as a result of dynamic, incremental changes in loading on the belt resulting from the user's foot impact on the belt.
2. Description of the Prior Art
Power driven exercise treadmills are well known, such as disclosed in Sweeney et al U.S. Pat. No. 4,842,266, wherein the treadmill has a power driven tread belt, the speed of which is manually selected and automatically maintained on a dynamic nominally constant basis and in which control commands are entered in a display panel and input to a microprocessor which in turn controls the drive motor speed. However, while such power driven treadmills are characteristically designed to be selectively speed variable, they also characteristically involve a compromise as to what may be termed tread belt "softness", i.e. the rate of restoration of nominal belt speed, i.e. rate of restabilization of a set, nominally constant speed when subject to so-called "foot plant" variations in belt loading and consequent dynamic change in belt speed.
A major cause of the stress and trauma associated with normal walking and running on a treadmill is known as "foot plant". "Foot plant" refers to the alternation of body weight from foot to foot as a user walks or runs on the moving tread belt. When the user does this, switching his or her body weight and support from one foot to the other, the user's forward motion is temporarily interrupted, introducing the possibility of subjecting the user's joints and muscles to stress and trauma. When the running surface can absorb some of the foot impact force, the stress is reduced, but there is also a risk of inconsistent support of the user if the tread surface is too "soft", i.e. where the variation in speed resulting from change in loading is too large.